1.01 posix message queue - JohnHau/mis GitHub Wiki

/*

  • server.c: Server program
  •       to demonstrate interprocess commnuication

  •       with POSIX message queues

*/

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h>

#include <fcntl.h> #include <sys/stat.h> #include <mqueue.h>

#define SERVER_QUEUE_NAME "/sp-example-server" #define QUEUE_PERMISSIONS 0660 #define MAX_MESSAGES 10 #define MAX_MSG_SIZE 256 #define MSG_BUFFER_SIZE MAX_MSG_SIZE + 10

int main (int argc, char **argv) { mqd_t qd_server, qd_client; // queue descriptors long token_number = 1; // next token to be given to client

printf ("Server: Hello, World!\n");

struct mq_attr attr;

attr.mq_flags = 0;
attr.mq_maxmsg = MAX_MESSAGES;
attr.mq_msgsize = MAX_MSG_SIZE;
attr.mq_curmsgs = 0;

if ((qd_server = mq_open (SERVER_QUEUE_NAME, O_RDONLY | O_CREAT, QUEUE_PERMISSIONS, &attr)) == -1) {
	perror ("Server: mq_open (server)");
	exit (1);
}
char in_buffer [MSG_BUFFER_SIZE];
char out_buffer [MSG_BUFFER_SIZE];

while (1) {

	memset(in_buffer,0,sizeof(in_buffer));
	// get the oldest message with highest priority
	if (mq_receive (qd_server, in_buffer, MSG_BUFFER_SIZE, NULL) == -1) {
		perror ("Server: mq_receive");
		exit (1);
	}

	printf ("Server: message received.\n");
	printf("in_buffer is %s\n",in_buffer);

	// send reply message to client

	if ((qd_client = mq_open (in_buffer, O_WRONLY)) == 1) {
		perror ("Server: Not able to open client queue");
		continue;
	}

	sprintf (out_buffer, "%ld", token_number);

	if (mq_send (qd_client, out_buffer, strlen (out_buffer) + 1, 0) == -1) {
		perror ("Server: Not able to send message to client");
		continue;
	}

	printf ("Server: response sent to client.\n");
	token_number++;
}

}`

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